1. Field of the Invention
The instant invention relates to an air induction assembly disposed in an intake passage through which air flows to an internal combustion engine. More specifically, the instant invention relates to the use of a plurality of flow conditioning elements to produce a uniform airflow with low turbulent fluctuations to the mass air flow sensor under all vehicle and engine speeds.
2. Description of the Related Art
It is known to those skilled in the art to use a mass air flow sensor, including those of the hot wire or hot film anemometry type, to measure the air flow rate entering an engine. The mass air flow sensor (MAFS) outputs an analog voltage signal that corresponds to the mass of air flowing through the air induction system. The output from the MAFS is used to maintain the desired air-fuel ratio so that performance, fuel economy and emission targets are met.
To provide an accurate indication of airflow, the MAFS must receive airflow of uniform velocity having a low magnitude of turbulent fluctuations over all engine and vehicle speeds. Airflow will exhibit some measure of turbulence and that turbulence can be described as the average fluctuation of the fluid from its average velocity.
When airflow having a high magnitude of turbulent fluctuations is presented to the MAFS, noise is created in the MAFS output signal as a direct indication of the airflow turbulence variation entering the MAFS. Much of this turbulence variation is caused from the ever present pulsation from the engine valve train and pistons. The pulsation creates signal noise which is particularly influential at low engine rpm.
Further, as with any fluid flow through a conduit, there is a considerable difference in the velocity between the airflow near the inner surface of the air induction duct and the airflow near the center of the air induction duct. This variation in velocity may be described as a parabola-like profile defining the relative velocity of the airflow within the air induction duct. The apex points downstream and the amplitude depends on the input velocity of the airflow. These airflow variations combine to increase fluctuations in the area adjacent to the MAFS, preventing consistent accurate measurements.
It is known to reduce the magnitude of the airflow turbulence variation by providing the air induction system with an air flow uniforming device upstream of the mass air sensor. Mollet, U.S. Pat. No. 4,397,192, teaches a mesh structure disposed within the air induction conduit perpendicular to the direction of the fluid flow and upstream from a sensor to provide a reduction in the oscillating air flow turbulence and provide a uniform flow of air across the sensor. However, as the mesh structure is disposed over the entire air induction conduit there is a corresponding restriction in the airflow which may pass through the mesh structure and to the engine. This decrease in airflow translates into a decrease in engine horsepower. Further, in addition to increased cost, the mesh structure may collect debris, corrode, or freeze, all of which again further restrict airflow and therefor engine horsepower.
It is further known to dispose within an air intake duct a swirl generating means with an air flow sensor mounted thereon. Takashima, U.S. Pat. No. 5,476,012, teaches a cone axially supported in the center of an air intake duct by guide vanes attached to the inner surface of the duct. Fixed to the downstream portion of the cone is the air flow sensor. The guide vanes are operative to swirl the air in cooperation with the cone.
The assembly taught by Takashima has the disadvantages of being difficult to fabricate and restricting the airflow provided to the engine. Further, as the airflow is swirling, the axial velocity of the airflow is reduced. The restricted and reduced velocity airflow therefor cause a corresponding decrease in engine horsepower. The instant invention provides uniform airflow with minimum restriction to the MAFS over all engine and vehicle speeds and does not generate a swirl therein. Further, the instant invention provides a structure which only partially extends into the airflow duct. This allows the manufacture of a simple and cost effective one piece design without the need for costly tooling.
Other variations of an airflow sensor supported in the air duct are taught by Woddbury, U.S. Pat. No. 5,481,925, and Kurrle, U.S. Pat. No. 4,602,515. Both of these references add the complexity of using the airflow sensor support members as airflow collecting pipes. The airflow sensor is not directly in the airflow path but is provided with airflow samples from the independent collecting pipes. The airflow is sampled over the cross section of the duct, and then travels radially inwardly to the centrally mounted airflow sensor pod. The airflow is therefor not conditioned prior to being provided to the air flow sensor located within the airflow path, but simply collected and fed to the air flow sensor.
It is desirable to create an airflow that has a uniform velocity and a low magnitude of turbulent fluctuations. It is further desirable to produce an air induction assembly that does not restrict the central portion of the air intake duct preventing a decrease in engine horsepower.